signalk-server
Version:
An implementation of a [Signal K](http://signalk.org) server for boats.
284 lines (243 loc) • 20 kB
HTML
<html lang="en" class="sidebar-visible no-js light">
<head>
<!-- Book generated using mdBook -->
<meta charset="UTF-8">
<title>Course Calculations - Signal K Server Documentation</title>
<!-- Custom HTML head -->
<meta name="description" content="A Guide for users and developers.">
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta name="theme-color" content="#ffffff" />
<link rel="shortcut icon" href="../../favicon.png">
<link rel="stylesheet" href="../../css/variables.css">
<link rel="stylesheet" href="../../css/general.css">
<link rel="stylesheet" href="../../css/chrome.css">
<link rel="stylesheet" href="../../css/print.css" media="print">
<!-- Fonts -->
<link rel="stylesheet" href="../../FontAwesome/css/font-awesome.css">
<link rel="stylesheet" href="../../fonts/fonts.css">
<!-- Highlight.js Stylesheets -->
<link rel="stylesheet" href="../../highlight.css">
<link rel="stylesheet" href="../../tomorrow-night.css">
<link rel="stylesheet" href="../../ayu-highlight.css">
<!-- Custom theme stylesheets -->
</head>
<body>
<div id="body-container">
<!-- Provide site root to javascript -->
<script>
var path_to_root = "../../";
var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? "navy" : "light";
</script>
<!-- Work around some values being stored in localStorage wrapped in quotes -->
<script>
try {
var theme = localStorage.getItem('mdbook-theme');
var sidebar = localStorage.getItem('mdbook-sidebar');
if (theme.startsWith('"') && theme.endsWith('"')) {
localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1));
}
if (sidebar.startsWith('"') && sidebar.endsWith('"')) {
localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1));
}
} catch (e) { }
</script>
<!-- Set the theme before any content is loaded, prevents flash -->
<script>
var theme;
try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { }
if (theme === null || theme === undefined) { theme = default_theme; }
var html = document.querySelector('html');
html.classList.remove('no-js')
html.classList.remove('light')
html.classList.add(theme);
html.classList.add('js');
</script>
<input type="checkbox" id="sidebar-toggle-anchor" class="hidden">
<!-- Hide / unhide sidebar before it is displayed -->
<script>
var html = document.querySelector('html');
var sidebar = null;
var sidebar_toggle = document.getElementById("sidebar-toggle-anchor");
if (document.body.clientWidth >= 1080) {
try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { }
sidebar = sidebar || 'visible';
} else {
sidebar = 'hidden';
}
sidebar_toggle.checked = sidebar === 'visible';
html.classList.remove('sidebar-visible');
html.classList.add("sidebar-" + sidebar);
</script>
<nav id="sidebar" class="sidebar" aria-label="Table of contents">
<div class="sidebar-scrollbox">
<a href="/" style="width:155px;height:30px;background-image:url(/signal-k-logo-image-text.svg);display:inline-block;background-repeat:no-repeat;background-position:center center;background-size:150px auto;"></a>
<ol class="chapter"><li class="chapter-item expanded affix "><a href="../../index.html">Introduction</a></li><li class="chapter-item expanded affix "><li class="part-title">Getting Started</li><li class="chapter-item expanded "><a href="../../installation/install.html"><strong aria-hidden="true">1.</strong> Installation</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../installation/raspberry_pi_installation.html"><strong aria-hidden="true">1.1.</strong> Installing on Raspberry Pi</a></li><li class="chapter-item expanded "><a href="../../installation/updating.html"><strong aria-hidden="true">1.2.</strong> Updating your installation</a></li><li class="chapter-item expanded "><a href="../../installation/command_line.html"><strong aria-hidden="true">1.3.</strong> Runtime environment & options</a></li></ol></li><li class="chapter-item expanded "><a href="../../security.html"><strong aria-hidden="true">2.</strong> Security</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../setup/generating_tokens.html"><strong aria-hidden="true">2.1.</strong> Generating tokens</a></li></ol></li><li class="chapter-item expanded "><li class="part-title">Setup</li><li class="chapter-item expanded "><a href="../../setup/configuration.html"><strong aria-hidden="true">3.</strong> Configuration</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../setup/seatalk/seatalk.html"><strong aria-hidden="true">3.1.</strong> Seatalk Connections</a></li></ol></li><li class="chapter-item expanded "><li class="part-title">Feature How Tos</li><li class="chapter-item expanded "><a href="../../features/anchoralarm/anchoralarm.html"><strong aria-hidden="true">4.</strong> Anchor Alarm</a></li><li class="chapter-item expanded "><a href="../../features/navdataserver/navdataserver.html"><strong aria-hidden="true">5.</strong> NMEA0183 Server</a></li><li class="chapter-item expanded "><a href="../../features/datalogging/datalogging.html"><strong aria-hidden="true">6.</strong> Data Logging</a></li><li class="chapter-item expanded affix "><li class="part-title">Support</li><li class="chapter-item expanded "><a href="../../support/help.html"><strong aria-hidden="true">7.</strong> Help & Support</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../support/faq.html"><strong aria-hidden="true">7.1.</strong> FAQs</a></li></ol></li><li class="chapter-item expanded "><a href="../../support/sponsor.html"><strong aria-hidden="true">8.</strong> Sponsor</a></li><li class="chapter-item expanded affix "><li class="part-title">Develop</li><li class="chapter-item expanded "><a href="../../develop/developer_notes.html"><strong aria-hidden="true">9.</strong> Notes for Developers</a></li><li class="chapter-item expanded "><a href="../../whats_new.html"><strong aria-hidden="true">10.</strong> What's New in V2</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../breaking_changes.html"><strong aria-hidden="true">10.1.</strong> Changes & Deprecations</a></li></ol></li><li class="chapter-item expanded "><a href="../../develop/webapps.html"><strong aria-hidden="true">11.</strong> WebApps</a></li><li class="chapter-item expanded "><a href="../../develop/plugins/server_plugin.html"><strong aria-hidden="true">12.</strong> Plugins</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../develop/plugins/deltas.html"><strong aria-hidden="true">12.1.</strong> Processing Data</a></li><li class="chapter-item expanded "><a href="../../develop/plugins/server_plugin_api.html"><strong aria-hidden="true">12.2.</strong> Server API</a></li><li class="chapter-item expanded "><a href="../../develop/plugins/resource_provider_plugins.html"><strong aria-hidden="true">12.3.</strong> Resource Providers</a></li><li class="chapter-item expanded "><a href="../../develop/rest-api/course_calculations.html" class="active"><strong aria-hidden="true">12.4.</strong> Course Providers</a></li><li class="chapter-item expanded "><a href="../../develop/plugins/autopilot_provider_plugins.html"><strong aria-hidden="true">12.5.</strong> Autopilot Providers</a></li></ol></li><li class="chapter-item expanded "><a href="../../develop/plugins/publishing.html"><strong aria-hidden="true">13.</strong> Publishing to the AppStore</a></li><li class="chapter-item expanded "><a href="../../develop/rest-api/open_api.html"><strong aria-hidden="true">14.</strong> REST APIs</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../develop/rest-api/course_api.html"><strong aria-hidden="true">14.1.</strong> Course API</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../../develop/rest-api/course_calculations.html" class="active"><strong aria-hidden="true">14.1.1.</strong> Course Calculations</a></li></ol></li><li class="chapter-item expanded "><a href="../../develop/rest-api/resources_api.html"><strong aria-hidden="true">14.2.</strong> Resources API</a></li><li class="chapter-item expanded "><a href="../../develop/rest-api/notifications_api.html"><strong aria-hidden="true">14.3.</strong> Notifications API</a></li><li class="chapter-item expanded "><a href="../../develop/rest-api/autopilot_api.html"><strong aria-hidden="true">14.4.</strong> Autopilot API</a></li><li class="chapter-item expanded "><a href="../../develop/rest-api/anchor_api.html"><strong aria-hidden="true">14.5.</strong> Anchor API</a></li></ol></li><li class="chapter-item expanded "><a href="../../develop/contributing.html"><strong aria-hidden="true">15.</strong> Contribute</a></li></ol>
</div>
<div id="sidebar-resize-handle" class="sidebar-resize-handle"></div>
</nav>
<!-- Track and set sidebar scroll position -->
<script>
var sidebarScrollbox = document.querySelector('#sidebar .sidebar-scrollbox');
sidebarScrollbox.addEventListener('click', function(e) {
if (e.target.tagName === 'A') {
sessionStorage.setItem('sidebar-scroll', sidebarScrollbox.scrollTop);
}
}, { passive: true });
var sidebarScrollTop = sessionStorage.getItem('sidebar-scroll');
sessionStorage.removeItem('sidebar-scroll');
if (sidebarScrollTop) {
// preserve sidebar scroll position when navigating via links within sidebar
sidebarScrollbox.scrollTop = sidebarScrollTop;
} else {
// scroll sidebar to current active section when navigating via "next/previous chapter" buttons
var activeSection = document.querySelector('#sidebar .active');
if (activeSection) {
activeSection.scrollIntoView({ block: 'center' });
}
}
</script>
<div id="page-wrapper" class="page-wrapper">
<div class="page">
<div id="menu-bar-hover-placeholder"></div>
<div id="menu-bar" class="menu-bar sticky">
<div class="left-buttons">
<label id="sidebar-toggle" class="icon-button" for="sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar">
<i class="fa fa-bars"></i>
</label>
<button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list">
<i class="fa fa-paint-brush"></i>
</button>
<ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu">
<li role="none"><button role="menuitem" class="theme" id="light">Light</button></li>
<li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li>
<li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li>
<li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li>
<li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li>
</ul>
<button id="search-toggle" class="icon-button" type="button" title="Search. (Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar">
<i class="fa fa-search"></i>
</button>
</div>
<h1 class="menu-title">Signal K Server Documentation</h1>
<div class="right-buttons">
<a href="../../print.html" title="Print this book" aria-label="Print this book">
<i id="print-button" class="fa fa-print"></i>
</a>
<a href="https://github.com/SignalK/signalk-server/tree/master/docs/src" title="Suggest an edit" aria-label="Suggest an edit">
<i id="git-edit-button" class="fa fa-edit"></i>
</a>
</div>
</div>
<div id="search-wrapper" class="hidden">
<form id="searchbar-outer" class="searchbar-outer">
<input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header">
</form>
<div id="searchresults-outer" class="searchresults-outer hidden">
<div id="searchresults-header" class="searchresults-header"></div>
<ul id="searchresults">
</ul>
</div>
</div>
<!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM -->
<script>
document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible');
document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible');
Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) {
link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1);
});
</script>
<div id="content" class="content">
<main>
<h1 id="course-calculations-and-providers"><a class="header" href="#course-calculations-and-providers">Course Calculations and Providers</a></h1>
<p>The <em>Course API</em> defines the path <code>/vessels/self/navigation/course/calcValues</code> to accommodate the calculated values related to course navigation.</p>
<p>These paths are available to be populated by a "course provider" plugin that uses the course information set using the <em>Course API</em>. This approach promotes the extensibility of Signal K server providing flexibility and interoperability. See <a href="#course-provider-plugins">Course Provider Plugins</a> below.</p>
<img src="../../img/course_provider.svg" width="300px"/>
<h2 id="calculated-value-paths-calcvalues"><a class="header" href="#calculated-value-paths-calcvalues">Calculated value paths: <code>calcValues</code></a></h2>
<p>The following paths are defined to hold values calculated using the information maintained by <em>Course API</em> operations:</p>
<ul>
<li>calcMethod: <em>("Rhumbline" or "GreatCircle")</em></li>
<li>crossTrackError</li>
<li>bearingTrackTrue</li>
<li>bearingTrackMagnetic</li>
<li>estimatedTimeOfArrival <em>(e.g. "2022-04-22T05:02:56.484Z")</em></li>
<li>distance</li>
<li>bearingTrue</li>
<li>bearingMagnetic</li>
<li>velocityMadeGood</li>
<li>timeToGo</li>
<li>targetSpeed</li>
<li>previousPoint.distance</li>
</ul>
<p><em>Example:</em></p>
<pre><code>{
"calcMethod": "Rhumbline",
"crossTrackError": 458.784,
"bearingTrackTrue": 4.58491,
"bearingTrackMagnetic": 4.51234,
"estimatedTimeOfArrival": "2022-04-22T05:02:56.484Z",
"distance": 10157,
"bearingTrue": 4.58491,
"bearingMagnetic": 4.51234,
"velocityMadeGood": 7.2653,
"timeToGo": 8491,
"targetSpeed": 2.2653,
"previousPoint": {
"distance": 10157
}
}
</code></pre>
<h2 id="course-notifications"><a class="header" href="#course-notifications">Course Notifications</a></h2>
<p>Calculated course values that cross a threshold should trigger a notification so that the necessary action can be taken.</p>
<p>The Course API defines the following notifications which should be implemented by a course provider:</p>
<ul>
<li><code>navigation.course.arrivalCircleEntered</code></li>
<li><code>navigation.course.perpendicularPassed</code></li>
</ul>
<h2 id="course-provider-plugins"><a class="header" href="#course-provider-plugins">Course Provider Plugins</a></h2>
<p>Signal K server includes the <code>Course Data Provider</code> plugin as part of the installation to provide out-of-the-box support for course calculations nd notifications.</p>
<p>This plugin can be replaced with others from the AppStore, or your own, to extend the number and types of calculations performed.</p>
<p>If you are looking to develop a course provider plugin, following are the recommended guidlines:</p>
<ol>
<li>Ensure values are generated for ALL the defined paths (above)</li>
<li>Values MUST be calculated using <code>/vessels/self/navigation/course</code> path values mainntained by the <em>Course API</em></li>
<li>Ensure values are set to null when no destination is set or the value cannot be calculated</li>
<li>Perform the calculations using a "worker thread" to minimise impact on the server "main thread"</li>
<li>Ensure the worker is set up and shut down as part of plugin "start" and "stop" functions</li>
<li>Raise the notifications outlined above.</li>
</ol>
</main>
<nav class="nav-wrapper" aria-label="Page navigation">
<!-- Mobile navigation buttons -->
<a rel="prev" href="../../develop/plugins/resource_provider_plugins.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
<a rel="next" href="../../develop/plugins/autopilot_provider_plugins.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
<div style="clear: both"></div>
</nav>
</div>
</div>
<nav class="nav-wide-wrapper" aria-label="Page navigation">
<a rel="prev" href="../../develop/plugins/resource_provider_plugins.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left">
<i class="fa fa-angle-left"></i>
</a>
<a rel="next" href="../../develop/plugins/autopilot_provider_plugins.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right">
<i class="fa fa-angle-right"></i>
</a>
</nav>
</div>
<script>
window.playground_copyable = true;
</script>
<script src="../../elasticlunr.min.js"></script>
<script src="../../mark.min.js"></script>
<script src="../../searcher.js"></script>
<script src="../../clipboard.min.js"></script>
<script src="../../highlight.js"></script>
<script src="../../book.js"></script>
<!-- Custom JS scripts -->
</div>
</body>
</html>